import tkinter as tk

window = tk.Tk()
window.title("my window")
window.geometry('400x200')

var = tk.StringVar()
l = tk.Label(window,textvariable=var, bg='green', font=('Arial', 12), width=15, height=2)

l.pack()

on_hit = False
def hit_me():
    global on_hit
    if(on_hit == False):
        on_hit = True
        var.set("You hit me")
    else:
        on_hit = False
        var.set("")

b = tk.Button(window, text='hit me', width=15, height=2, command=hit_me)

b.pack()


window.mainloop()




